1. Field of the Invention
This invention pertains generally to apparatus and a method for increasing efficiency and/or decreasing exhaust emissions of an internal combustion engine.
2. Discussion of the Prior Art
The concern over air pollution and the dwindling of petroleum resources has resulted in legislation which has caused a shift in emphasis from powerful, high compression engines to small, low compression ones. As the degree of pollution which an automobile introduces into the air is measured in parts per mile, a smaller, lower compression engine, burning a leaner mixture (i.e., a higher ratio of air to fuel) can more readily satisfy the pollution requirements.
It is known on the one hand that the level of CO (carbon monoxide) produced by the internal combustion engine decreases as the air-fuel ratio is increased, and continues to decrease beyond the "chemically ideal" ratio of 14.7, and the decrease extends to the "lean limit", i.e., the limit at which flame speed drops to zero and at which the air-fuel mixture does not ordinarily ignite. The production of NO.sub.x (oxides of nitrogen), on the other hand, is most sensitive to the time at which the spark is fired (given in degrees before top dead center, BTDC). The production of NO.sub.x in parts per mile, jumps from approximately 1,000 to 3,000 parts when the spark timing is advanced over a 20.degree. range. In order to reduce carbon monoxide, oxides of nitrogen and also other hydrocarbons, therefore, one must operate the internal combustion engine with an air-fuel ratio lying at the lean end of the scale, and ignite the mixture as close to TDC as possible. The difficulties associated with these conditions are two-fold: firstly, as the mixture is made leaner, it will become increasingly more difficult to ignite with the spark, since the spark constitutes a contant external energy source of approximately 0.1 joule/spark energy capacity, and secondly, the resultant drop in flame speed along with spark timing near TDC will result in late combustion of the mixture and hence reduced efficiency as well as increased discharge of unburnt hydrocarbons through the exhaust. (On the other hand it is known that in order to increase engine efficiency as well as decrease exhaust emissions it is very desirable to ignite and sustain combustion of a lean mixture in an internal combustion engine.)
One approach to this problem has been the so-called "CVCC" engine, which utilizes a pre-ignition chamber and an extra carburetor. However this technique has the disadvantage in that mechanical modification of the cylinders and engine is required.
Another approach is discussed in U.S. Pat. No. 2,457,973 issued Jan. 4, 1949 and entitled Ionizing Means and Methods of Ionization. This patent teaches how to effect ionization of a gaseous mixture in the combustion chamber of an internal combustion engine by utilizing in combination with a conventional spark plug a radium cell in close proximity to the firing electrodes and an auxiliary electrode. It can readily be appreciated that, while such a device may reduce the firing potential near the vicinity of the electrode and perhaps extend spark plug life, flame velocity is not increased and it appears that flames propagating in air fuel mixtures below the lean limit will be quenched.
Another apparatus for producing an electric space charge or ionization in the combustion chamber of reciprocating piston type or turbine type combustion engines is disclosed in U.S. Pat. No. 2,766,582 issued Oct. 16, 1956, entitled Apparatus for Creating Electric Space Changes in Combustion Engines. This patent teaches the production of electric space charges in combustible fuel and air mixtures by electrically charging a dielectric type liquid fuel previous to jet spraying from an engine carburetor nozzle or from a spray nozzle in the combustion chamber proper. The electrically charged fuel is subsequently evaporated in space in the combustion chamber. A particular disadvantage of this technique is the generation of space charges in the fuel prior to its injection in the cylinder. This leads to a complex charge generating mechanism and a complex fuel transporting and injecting mechanism into the combustion chamber so as to maintain the charges that were generated in the fuel. Also additional insulating mechanisms are required to prevent charge leakage.
Another prior art device, which provides another means of sparking in an internal combustion engine, is the internal combustion engine ignition system disclosed in U.S. Pat. No. 2,617,841 issued Nov. 11, 1952. This patent discloses an ignition system for internal combustion engines which utilizes "voltages of ultra-high frequency for sparking." (Column 1, lines 3-4.) The teaching of this patent "contemplates that an internal combustion engine be fired by the method comprising the steps of generating high frequency energy, applying the energy to a resonator or resonant circuit, and tuning to the frequency of this energy the resonant circuit in timed relationship with the movable wall member to cause a spark to leap a spark gap in the circuit at resonance of the resonator." (Column 2, lines 43-50, and column 3, line 1.) The main disadvantages of this approach are as follows: (1) since its purpose is to produce the initial breakdown of the air-fuel mixture very high power high frequency devices are necessary to initiate ignition in the cylinder, and accordingly pulse type peak power ignition is necessary, as a practical matter, to handle the power required, and therefore flame speed or avoidance of flame quenching is not necessarily enhanced because of the short duration of the high frequency energy for ignition; (2) energy is coupled to a tuned resonant cavity in which resonance varies, thus requiring precise and complicated timing mechanisms; (3) extensive modification of cylinder design and engine design is necessary; and (4) since ignition occurs as the cylinder volume is decreasing, and not increasing, one will encounter many cavity resonant frequencies before reaching the desired one and considerable pains will have to be taken to insure that ignition does not occur as these other resonant modes are passed.
In view of the foregoing it is a principal object of the present invention to provide a system which increases the efficiency and also reduces the exhaust emissions of an internal combustion engine which can be installed in existing internal combustion engines, with a minimum of engine modification, and is relatively cheap and easy to manufacture and install, and requires relatively low power in operation.
Other objects are to enhance combustion and increase flame speed in the combustion chambers of internal combustion engines and to provide an improved ignition support system for an internal combustion engine.
Other objects and advantages of the invention will become apparent from the following description of particular preferred embodiments of the invention when read in conjunction with the accompanying drawings.